Project Summary: To address widespread public concern about the health effects from air pollution in London and to alleviate traffic congestion, the Mayor of London introduced the Congestion Charge Scheme (CCS) in central London in February 2003. Research on the impact of the CCS on air quality and the oxidative potential of particulate air pollution is currently underway. However, the potential health impacts of reduced traffic related air pollution due to the CCS have not been previously investigated. The proposed research directly addresses this gap by evaluating 1) whether the introduction of the CCS had an impact on morbidity and mortality and 2) whether this impact can be explained by changes in traffic related air pollution, and 3) whether changes in exposure to air pollution resulting from the CCS are equitably distributed across areas with varying levels of socioeconomic deprivation. To address the first aim,the change in rates of hospitalizations and deaths over the three years prior to and following the introduction of the CCS will be compared between areas affected by the CCS and surrounding areas. Changes in traffic related air pollution will be estimated using an emission-dispersion model that incorporates extensive data on traffic volume, vehicle type, and speed. Regression analysis will be used to evaluate whether the estimated change in traffic related air pollution explains the pre versus post-CCS change in rates of hospitalizations or deaths in the second aim. Potential social inequalities in the estimated reduction in traffic related air pollution will be quantified using a variety of measures of inequality to address the thirdaim. Relevance: The introduction of the CCS represents a rare experimental setting for studying the health impacts of changes in traffic related air pollution. To date there have been few investigations of the health effects of reduced air pollution exposure resulting from a policy intervention; furthermore, none focused specifically on reduced traffic emissions within a clearly geographically defined area such as in London. Urban centers in the US facing growing congestion problems are likely to consider traffic management programs similar to the London CCS. The proposed research would provide useful insight into the potential of such traffic management strategies as important public health interventions.